update image naming scheme, compatibility with ggcr v0.15.2

[puerco]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

This PR modifies the default naming scheme used in SPDX packages when representing container images. The new scheme will now be the expanded image reference @ digest when available. For example the top-level package representing nginx will now be:

    index.docker.io/library/nginx@sha256:480868e8c8c797794257e2abd88d0f9a8809b2fe956cbfbc05dcc0bca1f7cd43

When no reference is available, the name of the package will still be the digest as in sha256:63547654...

Multi-arch images fronted by the index manifest will be named using the same schema while layers keep the digest naming convention. Here is a sample:

 📂 SPDX Document SBOM-SPDX-c03bb1e1-b939-4fed-b3e5-66d698dfdb76
  │ 
  │ 📦 DESCRIBES 1 Packages
  │ 
  ├ index.docker.io/library/nginx@sha256:480868e8c8c797794257e2abd88d0f9a8809b2fe956cbfbc05dcc0bca1f7cd43
  │  │ 🔗 8 Relationships
  │  ├ CONTAINS PACKAGE index.docker.io/library/nginx@sha256:573aeafa0c5883bb8f93516fe904b47057b4fba547ad310c6967f563e5a2bb07
  │  │  │ 🔗 7 Relationships
  │  │  ├ CONTAINS PACKAGE sha256:9c7c4e67baad3ce38491ce8c1ffaa9ca9ce37409270ce53ab3472054f35d097e
  │  │  ├ CONTAINS PACKAGE sha256:b4d3566b2dd3e77d74d603c6edfdca033ecac6379238258a3ba8ace3a17aa818
  │  │  │  │ 🔗 141 Relationships
  │  │  │  ├ CONTAINS PACKAGE adduser@3.118
  │  │  │  ├ CONTAINS PACKAGE apt@2.2.4
  │  │  │  ├ CONTAINS PACKAGE base-files@11.1+deb11u7
  │  │  │  ├ CONTAINS PACKAGE base-passwd@3.5.51
  │  │  │  ├ CONTAINS PACKAGE bash@5.1-2+deb11

Which issue(s) this PR fixes:

This PR also fixes an incompatibility with go-containerregistro v0.15.x that was preventing updating the library.

Special notes for your reviewer:

/assign @cpanato

Does this PR introduce a user-facing change?

SPDX packages representing container images are now named using their full reference and digest: `registry.com/repository/image@sha256:digest`

[cpanato]

@puerco needs rebase

[cpanato]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato, puerco

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[cpanato]

/lgtm